Inductive apparatus with magnetic locking plates

ABSTRACT

Electrical inductive apparatus including a magnetic core constructed of stacked-magnetic laminations arranged to provide a plurality of spaced-leg portions, the adjacent ends of which are joined by first and second yoke portions. Yoke clamps are disposed to hold the first and second yoke portions in assembled relation, and a plurality of lock plate members are disposed against the leg portions. The lock plate members, which mechanically link the yoke clamps, are constructed of a plurality of magnetic laminations whose major surfaces are disposed perpendicular to the major surfaces of the laminations in the leg portions.

United States Patent [72] Inventor Selwyn Palmer Waterdown, Ontario, Canada [21] Appl. No. 75,216 [22] Filed Sept. 24, 1970 [45] Patented Oct. 19, 1971 [73] Assignee Canadian Westinghouse Company, Limited Hamilton, Ontario, Canada [54] I INDUCTIV E APPARATUS WITH MAGNETIC LOCKING PLATES 4 Claims, 3 Drawing Figs.

[52] U.S.Cl 336/210, 336/212, 336/219 [51] Int. Cl 11011 27/26 [50] Field of Search 336/84,

[5 6] References Cited UNITED STATES PATENTS 1,610,867 12/1926 Lennox 336/212 2,370,045 2/1945 Keto 336/84 2,910,663 10/1959 Wilk et al. 336/210 3,349,357 10/1967 McNutt et al 336/210 3,419,836 12/1968 Aldridge,Jr 336/210 Primary Examiner-Thomas J. Kozma AttorneysA. T. Stratton, F. E. Browder and D. R, Lackey ABSTRACT: Electrical inductive apparatus including a magnetic core constructed of stacked-magnetic laminations arranged to provide a plurality of spaced-leg portions, the adjacent ends of which are joined by first and second yoke portions. Yoke clamps are disposed to hold the first and second yoke portions in assembled relation, and a plurality of lock plate members are disposed against the leg portions. The lock plate members, which mechanically link the yoke clamps, are constructed of a plurality of magnetic laminations whose major surfaces are disposed perpendicular to the major surfaces of the laminations in the leg portions.

INDUCTIVE APPARATUS WITH MAGNETIC LOCKING PLATES BACKGROUND OF THE HJVENTION 1. Field of the Invention The invention relates in general to electrical inductive apparatus, such as power transformers, and more specifically to electrical inductive apparatus of the coreform type.

2. Description of the Prior Art Electrical inductive apparatus of the core-form type, such as power transformers and reactors, utilize a plurality of stacked, superposed layers of magnetic laminations, to provide the desired plurality of spaced, winding leg portions and upper and lower yoke portions which interconnect the adjacent ends of the leg portions. The upper and lower yoke portions are each clamped together with suitable yoke-clamping means, such as by a pair of channel members held by bolts which either pass through, or adjacent the ends of the yoke laminations.

When the core-winding assembly of a transformer is moved during assembly, it is lifted by attaching the lifting harness to lugs or crossmembers connected to the upper yoke-clamping means, and when the windings of the transformer are subjected to a short circuit, the windings exert axial forces which tend to separate the upper and lower yokes and the yokeclamping members. The laminations in the leg portions of small transformers are able to withstand the tensile stresses created therein by lifting the transformer, and also due to short circuits, but in larger power transformers these stresses adversely affect the magnetic properties of the core material, and damage the insulation disposed about compression bolts disposed through openings in the laminations. Thus, some means is provided for mechanically linking the upper and lower yoke-clamping means, which means takes the lifting and short circuit stresses, in preference to the laminations of the leg portions.

In the prior art, the linking means may be tie rods or bolts of circular section, or metallic plates disposed on each side of each leg portion, which are fixed to the upper and lower yoke portions. If rods or bolts are used, and they are placed outside the winding, they present insulation problems in high voltage transformers. Ifthey are placed between the leg portions and the windings, the diameter of the opening in the windings, and thus the outer diameter of the windings, must be increased, increasing the size and cost of the apparatus.

Metallic plates, usually called lock plates, are suitable for medium power transformers, but the leakage field component directed at right angles to the axis of the leg portions increases with the transformer rating and voltage, producing an intolerable localized heating of the lock plates, as well as a load loss by leakage flux returning down the lock plate. Using nonmagnetic metals reduces the heating and losses, but transformer ratings are reached where even nonmagnetic metals are excessively heated by the leakage flux. Nonmetallic lock plates are too costly, and must be made thicker than metal lock plates for the same tensile strength, requiring larger coils or windings. Further, nonmetallic lock plates allow the leakage flux to strike the laminations of the leg portions perpendicular to their major surfaces, causing localized overheating of the leg portions.

Thus, it would be desirable to provide new and improved electrical inductive apparatus of the core-form type having lock plates for reducing the tensile stresses in the laminations of the leg portions of the magnetic core, which lock plates are not subject to overheating, which do not create substantial load losses, which have a high-tensile strength without requiring a large cross-sectional area, which protect the laminations in the leg portions of the core from overheating, and which may be manufactured for a relatively low cost.

SUMMARY OF THE INVENTION Briefly, the present invention is new and improved electrical inductive apparatus of the core-form type, having a magnetic core which includes a plurality of stacked layers of magnetic laminations, arranged to provide a plurality of leg portions, and first and second yoke portions which connect the adjacent ends of the leg portions. First and second yoke-clamping means hold the laminations of the first and second yoke portions respectively, in assembled relation, and lock plate members, disposed on opposite sides of the leg portions, mechanically link the first and second yoke-clamping means to prevent undue tensile stresses from being created in the laminations of the leg portions, when the magnetic core is lifted, and when it is subjected to short circuit stresses.

The lock plate members are constructed of a plurality of magnetic laminations bonded together with a suitable adhesive, with the major surfaces of the laminations in the lock plate members being disposed perpendicular to the major surfaces of the laminations in the leg portions. The laminated lock plate members have a high-tensile strength, they may be manufactured for a relatively low cost, they substantially reduce load losses, they substantially reduce localized heating in the lock plate members, and they eliminate localized heating of the laminations in the leg portions of the magnetic core.

BRIEF DESCRIPTION OF THE DRAWINGS The invention may be more readily understood when considered in view of the following detailed description of exemplary embodiments thereof, taken with the accompanying drawings, in which:

FIG. 1 is a perspective view, partially cut away, and partially in section, of a power transformer constructed according to the teachings of the invention;

FIG. 2 is a perspective view of a lock plate which is constructed according to the teachings of the invention and used in the transformer shown in FIG. 1; and

FIG. 2A is a fragmentary perspective view of a lock plate constructed according to another embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings and FIG. 1 in particular, there is shown a perspective view, partially cut away, and partially in section, of a power transformer 10 of the core-form type, which includes a magnetic core-winding assembly 12 disposed in an enclosure or tank 14, which is filled to a predetermined level 16 with an insulating and cooling liquid dielectric, such as mineral oil or askarel. Coolers or heat exchangers 18 are connected to the tank 14, with the liquid dielectric circulating upwardly through the core-winding assembly 12, through the coolers l8, and back to the tank 14. Transformer 10, in this example, is a three-phase transformer having a magnetic core 20 and a plurality of phase-winding assemblies, with only phase-winding assembly 22 being shown in order to more clearly illustrate the construction of the magnetic core. Each phase-winding assembly includes high and low voltage windings concentrically disposed about a winding leg of the magnetic cores 20, with the high-voltage windings each being connected to a high-voltage bushing, such as highvoltage bushing 24, with the remaining high-voltage bushings being mounted in openings 26 and 28. The low-voltage are each connected to a low-voltage bushing, with the low-voltage bushings being disposed on the portion of the tank cover which is cut away in FIG. 1.

The magnetic core 20 is formed of a plurality of stacked layers of metallic, magnetic laminations, such as grain oriented silicon steel, which have their major surfaces disposed in contacting relation. The layers of laminations are arranged to provide three leg portions, of which two leg portions 30 and 32 are clearly shown in FIG. 1, with the leg portions being disposed in spaced, parallel relation, and each having upper and lower ends. Upper and lower yoke portions 34 and 36 are also provided, which interconnect the upper ends, and the lower ends, respectively, of the leg portions.

The leg portions 30 and 32 are illustrated as having a cruciform cross-sectional configuration, in which the widths of the laminations are progressively changed across the stack to more nearly approximate a round cross-sectional configuration, for use with round coils or windings, However, the core leg portions may have other cross-sectional configurations, such as square or rectangular, as required by the specific application.

The upper and lower yoke portions 34 and 36 have yokeclamping means 38 and 40, respectively, each having a pair of channel members disposed on opposite sides of their associated yoke portion. Yoke-clamping means 38 has channel members 42 and 44 disposed adjacent the major surfaces of the outer laminations of the upper yoke portion 34, and yokeclamping means 40 has channel members 46 and 48 and disposed adjacent the major surfaces of the outer laminations of the lower yoke portion 36.

In order to protect the laminations of the leg portions from excessive tensile stresses, such as produced by lifting the magnetic core-winding assembly 12 by apparatus connnected to the upper yoke-clamping means 38, and by axial forces produced by the phase windings during a short circuit which tend to force the yoke portions away from the ends of the leg portions, a plurality of lock plate members 50, 52 and 54 are dispose to mechanically link channel members 42 and 46, and a plurality of lock plate members 56, 58, and 60 are disposed to mechanically link channel members 44 and 48.

The lock plate members are disposed in contacting relation with the major surfaces of the outermost laminations of the leg portions, with lock plate members 50 and 56 being disposed on opposite sides of leg portion 32, lock plate members 52 and 58 disposed on opposite sides of leg portion 30, and lock plate members 54 and 60 disposed on opposite sides of the remaining leg portion.

The laminations of the leg portions are compressed by bolts or rods disposed through openings in the leg laminations and lock plates, such as by bolt 62 shown disposed through transverse openings disposed through the laminations of the leg portion 32; or, by nonmetallic bands disposed around the leg laminations and lock plates, or through openings in the leg laminations and lock plates, as desired.

The upper and lower yoke-clamping means are mechanically linked by welding the lock plate members directly to the upper and lower yoke-clamping members; or, by disposing metallic plates or pads on the lock plate members, which cooperate with similar plates or pads disposed on the yokeclamping members to subject the lock plates to tensile stresses instead of the laminations of the yoke portions. In the latter embodiment, illustrated in FIG. 1, metallic plates or pads are welded adjacent each end of the lock plates, such as pads 64 and 66 on lock plate 50, and pad 68 on lock plate 52, pad the two pads on each lock plate being onthe same major side or surface thereof, and adjacent the channel members of the yoke-clamping means.

Each of the channel members have plates or pads welded thereto, which, when the phase windings are compressed between pressure plates (not shown) disposed at each axial end of each phase winding, are aligned with the pads on the lock plates such that the pads on the upper yoke-clamping means are immediately below and in contacting relation with the upper pads on the lock plate members, and the pads on the lower yoke-clamping means are immediately above and in contacting relation with the lower pads on the lock plate members. Thus, as illustrated in FIG. 1, channel member 42 has three pads welded thereto, such as pad 70, which is immediately below and in contact with pad 68 on lock plate member 52, and channel member 46 has three pads, such as pad 72, which is immediately above and in contact with the lower pad 66' on lock plate member 50. The vertically aligned pads on the upper and lower yoke channel members, being inside" the two pads on each locking plate, thus transmit 'short circuit forces which tend to raise the upper yoke porin preference to the laminations of the leg portions of the magnetic cores. Further, the lower pads on the lock plate, being below the pads on the lower yoke-clamping means, absorb and transmit the tensile stresses to the lock plate members, when the magnetic corewinding assembly 12 is lifted by lifting means which is attached to the upper yoke-clamping means.

The construction of the lock plate members is critical in large power transformers. The lock plates, for example, may be constructed of mild steel up to predetermined ratings without serious overheating of the lock plate members and excessive load losses due to leakage magnetic flux, but in higher ratings the heating and losses become substantial. Localized heating of the lock plate may become especially severe, and intolerable, when the windings are axially split and interconnected via switching means. As the turns of the split windings are tapped out, a localized unbalance of ampere turns is created which causes a leakage flux circulation adjacent the tapped out portions of the winding, which flux strikes the lock plate members with an angle that is substantially perpendicular to their major surfaces. FIG. 2 is a perspective view of the lock plate member 50 shown in FIG. 1, illustrating leakage flux lines and how they link or strike the lock plate member, producing heating and losses therein.

Nonmagnetic, metallic materials, while exhibiting less heating and losses then mild steel for any specific rating, reach a level of intolerable heating at higher transfonner ratings. Nonmetallic materials must have large cross-sectional areas to provide the desired tensile strength, and thus are costly, and they do not shield the laminations of the leg portions from the leakage magnetic flux, with heating and losses occurring in the leg laminations due to the leakage flux striking the major sur faces of the leg laminations in a substantially perpendicular manner.

FIG. 2 illustrates a construction for lock plate member 50, which solves the problems associated with lock plates of the prior art, having a plurality of metallic, magnetic laminations 82 stacked with their major surfaces together, and bonded into unitary structure with a suitable adhesive. The portion of lock plate member 50 within circle 84 is shown enlarged and cross-hatched at circle 84', in order to more clearly illustrate the laminations 82, separated by bonding or adhesive means 86.

The laminations 82 have a width dimension selected to provide the desired tensile strength, a length dimension 92 selected according to the core height, and a thickness dimension selected from the standpoint of strength, cost of materials, and assembly time, A thickness of about 12-25 mils is suitable, but other thickness dimensions may be used. The magnetic material does not necessarily have to be grain oriented. Grain oriented steel, however, my be used, as it would provide a lower reluctance path for shielding the leg portions from the leakage magnetic flux, than laminations formed of nongrain oriented steel.

The adhesive or bonding means 86 may be any suitable resin which is compatible with the temperature and chemical environment inside the electrical apparatus with the adhesives of the epoxy type being excellent for power transformers of the type filled with mineral oil or askarel.

FIG. 2A is a fragmentary perspective view of a lock plate member 50' constructed according to another embodiment of the invention, in which a solid metallic extension 65 is welded, or otherwise fixed, to each end of the lock plate. The extension 65 includes a solid metallic pad 67 which functions similar to the pads 64 and 66 shown in FIG. 2.

In constructing the lock plate members, such as lock plate member 50, the laminations may be assembled, dipped into the bonding means and removed, and then clamped in a suitable form while the bonding means is being cured, such as in an oven at an elevated temperature, Another method would be to brush on a thin coating of the bonding means on the major surfaces of the laminations as they are being assembled.

The bonding means facilitates the handling of the lock plate and it also provides a unitary assembly in which the tensile stresses are more uniformly shared by the plurality of stacked laminations. if the laminations of the lock plates are not bonded into a unitary assembly, certain of the laminations may be subjected to greater tensile stresses than others, due to manufacturing tolerances in the laminations, and thus they may fail and transmit the tensile stresses to still other laminations which may set up a progressive failure of the lock plate member.

The pads 64 and 66 are welded to the laminations of the laminations 82, as illustrated in FIG. 2, and the pads may be constructed of a mild steel, or preferably of a nonmagnetic stainless steel, to reduce localized heating in the pads.

It is important to note that the major surfaces of the laminations 82 in the lock plate members are disposed perpendicular to the major surfaces of the laminations in the leg portions. Thus, the leakage field strikers the edges of the laminations 86, substantially reducing eddy and circulating currents in the lock plate members, and therefore substantially reducing heating and losses in the lock plate members. The laminations of the lock plate members shield the laminations of the adjacent leg portions from the leakage field, preventing the heating thereof, as they provide a low-reluctance path in shunt with the leg portions, between the leg portions and the leakage magnetic field.

in summary, there has been disclosed new and improved electrical inductive apparatus of the core-form type, which protects the laminations of the leg portions from being deleteriously stressed, which would adversely affect the magnetic properties of the leg portions, as well as damaging the insulation disposed around the bolts or tie rods, if used to compress the laminations, These features are produced by new and improved laminated lock plate members which link the upper and lower yoke-clamping means and absorb tensile stresses produced by lifting the magnetic-core winding assembly, and also by short circuit stresses, in preference to stressing the laminations of the leg portions. The laminated lock plate members have the major surfaces of their laminations disposed perpendicular to the major surfaces of the laminations of the leg portions of the magnetic core, with the thin edges of the laminations of the lock plate members being disposed such that the leakage magnetic field strikes the edges in a substantially vertical manner, reducing the magnitude of eddy and circulating currents in the lock plate members, and thus reducing the heating and losses therein. The laminated magnetic lock plate members also provide a low-reluctance magnetic path adjacent the leg portions of the magnetic core, preventing the leakage magnetic flux from linking the major surfaces of the outer laminations of the leg portions, reducing the heating and losses in the leg portions of the magnetic core.

I claim as my invention:

1. Electrical inductive apparatus comprising:

a magnetic core having a plurality of metallic, magnetic laminations stacked with their major surfaces in contacting relation, sad magnetic core including a plurality of spaced-leg portions, each having first and second ends, and first and second yoke portions which interconnect the first ends, and the second ends, respectively, of said leg portions,

a plurality of electrical windings dispose about at least certain of said leg portions,

first and second yoke-clampng means disposed to hold said first and second yoke portions, respectively, in assembled relation, each of said first and second yoke-clamping means including first and second yoke-clamping members disposed on opposite sides of their associated yoke portion, adjacent the major surfaces of the outer yoke laminations,

a plurality of first locking members disposed to mechanically link the first yoke-clamping members of said first and second yoke-clamping means. absorbing forces which tend to separate the first and second yoke portions in preference to laminations of the le portions, a plurality of second locking members isposed to mechanically link the second yoke-clamping members of said first and second yoke-clamping means, absorbing forces which tend to separate the first and second yoke portions in preference to laminations of the leg portions,

said first and second locking members being disposed on opposite sides of said leg portions, against the major surfaces of the outer laminations thereof, with their ends extending between yoke-clamping members of said first and second yoke-clamping means and their associated yoke portions,

each of said first an second locking members including a plurality of metallic, magnetic laminations stacked with their major surfaces in contacting relation, and oriented with respect to their associated leg portions such that the major surfaces of the laminations in said locking members are substantially perpendicular to the major surfaces of the laminations in said leg portions.

2. The electrical inductive apparatus of claim 1 including adhesive means disposed to bond the laminations in each of the locking members together.

3. The electrical inductive apparatus of claim 1 including metallic pads fixed to the locking members and to the first and second clamping members of the first and second yoke-clamping means, the metallic pads on the locking members cooperating with the metallic pads on the clamping members to mechanically stress the locking members in preference to the leg portions of the magnetic core, when the magnetic core is lifted and subjected to short circuit stresses.

4. The electrical inductive apparatus of claim 1 wherein the metallic, magnetic laminations of the first and second locking members are welded directly to the first and second yokeclamping members, respectively, of the first and second yokeclamping means. 

1. Electrical inductive apparatus comprising: a magnetic core having a plurality of metallic, magnetic laminations stacked with their major surfaces in contacting relation, sad magnetic core including a plurality of spaced-leg portions, each having first and second ends, and first and second yoke portions which interconnect the first ends, and the second ends, respectively, of said leg portions, a plurality of electrical windings dispose about at least certain of said leg portions, first and second yoke-clampng means disposed to hold said first and second yoke portions, respectively, in assembled relation, each of said first and second yoke-clamping means including first and second yoke-clamping members disposed on opposite sides of their associated yoke portion, adjacent the major surfaces of the outer yoke laminations, a plurality of first locking members disposed to mechanically link the first yoke-clamping members of said first and second yoke-clamping means. absorbing forces which tend to separate the first and second yoke portions in preference to laminations of the leg portions, a plurality of second locking members disposed to mechanically link the second yoke-clamping members of said first and second yoke-clamping means, absorbing forces which tend to separate the first and second yoke portions in preference to laminations of the leg portions, said first and second locking members being disposed on opposite sides of said leg portions, against the major surfaces of the outer laminations thereof, with their ends extending between yoke-clamping members of said first and second yoke-clamping means and their associated yoke portions, each of said first an second locking members including a plurality of metallic, magnetic laminations stacked with their major surfaces in contacting relation, and oriented with respect to their associated leg portions such that the major surfaces of the laminations in said locking members are substantially perpendicular to the major surfaces of the laminations in said leg portions.
 2. The electrical inductive apparatus of claim 1 including adhesive means disposed to bond the laminations in each of the locking members together.
 2. The electrical inductive apparatus of claim 1 including adhesive means disposed to bond the laminations in each of the locking members together.
 3. The electrical inductive apparatus of claim 1 including metallic pads fixed to the locking members and to the first and second clamping members of the first and second yoke-clamping means, the metallic pads on the locking members cooperating with the metallic pads on the clamping members to mechanically stress the locking members in preference to the leg portions of the magnetic core, when the magnetic core is lifted and subjected to short circuit stresses.
 4. The electrical inductive apparatus of claim 1 wherein the metallic, magnetic laminations of the first and second locking members are welded directly to the first and second yoke-clamping members, respectively, of the first and second yoke-clamping means. 